Liquid fuel injection pumps

ABSTRACT

A LIQUID FUEL PUMP INCLUDING A PLUNGER WHICH HAS A GENERALLY HELICAL ESCAPE CHANNEL FORMED IN ITS PERIPHERY. THE BOTTOM, THAT IS THE BASE, OF THE CHANNEL IS FORMED SO AS TO BE OF A PROGRESSIVELY VARYING DEPTH ACROSS THE WIDTH OF THE CHANNEL.

Jan. 5, 1971 p 5, CURRAN EI'AL I 3,552,889

LIQUID FUEL INJECTION PUMPS Filed Feb. 25, 1969 INVENTOR: J.I.S. (IURRAN 1.

.LR. HU'IIIANI) United States Patent US. Cl. 417-494 6 Claims ABSTRACT OF THE DISCLOSURE A liquid fuel pump including a plunger which has a generally helical escape channel formed in its periphery. The bottom, that is the base, of the channel is formed so as to be of a progressively varying depth across the width of the channel.

BACKGROUND OF THE INVENTION The invention pertains to liquid pumps of the type having a cam operated plunger piston within a cylinder whereby the piston is driven with a reciprocatory movement to pump liquid. The piston has a helical channel in its periphery, which channel has a control edge that is arranged to register with a port in the cylinder wall during a pumping stroke to thereby terminate the delivery of fuel from the pumping chamber by release of the pressure from the chamber.

Such a prior art device is shown to the US. Pat. No. 3,435,770 issued Apr. 1, 1969, to A. J. Ellis, entitled Liquid Fuel Injector Pumps, and which has been assigned to an assignee common with the present invention. That patent is concerned with the shape of the control edge of the channel for modifying the rate of pressure decay. This is done by the formation of a shallow step at the helical or similarly shaped control edge of the known channel formation, providing in effect, primary and secondary control edges, the depth at least of the said shallow step providing a new variable design factor in the control of pressure decay at the end of pump delivery.

It has been proposed that the base of the said shallow step could be made other than as hitherto for the channel itself (ie flat or cylindrically) coaxial with the common axis of the piston and cylinder as being another variable factor of design relevant to the control of pressure decay.

SUMMARY OF THE INVENTION The present invention obtains further control by further constructional modification using the principle embodied in the shallow step aforesaid, and is an improvement of the shallow step principle.

The present invention provides a fluid injector pump of the type having a pumping piston with a generally helical, pressure escape channel including a control edge along one side thereof, the channel also having a bottom that becomes progressively deeper as it extends from that side of the channel containing the control edge of the channel.

According to the present invention the improved pump of the kind referred to is characterized by a plurality of shallow steps, extending from the primary control edge towards the opposite limit of the escape channel in the periphery of the piston, initially defined by such primary control edge and so proportioned as to progressively vary the effective flow area through the complementary escape port in the cylinder wall to provide an instantaneous pressure decay rate of not more than 350 kgm/cmF/millisecond and not less than 70 kgm./cm. /rnillisec0nd.

3,552,889 Patented Jan. 5, 1971 The expression plurality of shallow steps is used herein to include a finite or infinite number of steps so that in the latter case the transverse shape of the bottom or base of said escape passage progressively varies in depth to modify pressure decay relative to a complementary port-like exit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal, cross sectional view through a pump embodying the present invention; and

FIG. 2 is a fragmentary cross sectional view along line AA of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT As shown in the drawings, the cylindrical wall of the pump piston 11 is formed with a channel passage 14 open at all times to the pump chamber, said channel being defined by a primary or upper control edge 13a which has a substantially helical form. The bottom or base 21 of the channel (see FIG. 2) is shaped so that its radial depth is a minimum at the primary control edge 13a, increasing progressively towards the opposite defining edge 13b. The shape thus produced is in principle an infinite number of infinitely small steps, but the invention includes relatively larger and more clearly defined steps providing approximately the same mean angle or slope, the width and radial depth of which may be equal or unequal and the radial difference factor may be relatively positive or negative. The channel may also vary in width along its length as another design variable.

The pump piston 11 is contained within a pump cylinder 10 in which are formed diametrically opposed ports 17. A delivery valve 12 is provided above the pump cylinder 10 and this communicates with a conduit 16 for de livery of fuel from the pump.

The channel passage 14 communicates at all times with the pump chamber via a longitudinal groove 15 in the piston 11.

At the end of the pump piston opposite to that nearest the delivery valve 12 is provided a pump plunger head 11a complementary to an actuating cam (not shown) by means of which the pump piston is reciprocated.

A toothed sequent 11b is provided adjacent the pump plunger head 11a and this co-operates with a rack (not shown) by means of which the rotational position of the pump piston 11 within the cylinder 10 can be adjusted. In addition, a return spring means (not shown) is provided for the pump piston. The rotational position of the pump piston 11 determines the movement of the piston required to cause opening and closing of the ports 17 in the cylinder 10.

' In a specific example, a pump generally in accordance with the illustration FIG. 1, operating at 214 strokes per minute, having a piston stroke of 22 mm. and piston diameter of 24 mm., a delivery valve of 250 cubic mm. unloading volume, delivering 3750 cubic mm. of liquid fuel at a peak pressure of approximately 700 kgm./sq. cm. having two ports 6 mm. diameter in the cylinder complementary to and coacting with two helical escape grooves in the piston periphery each 6.35 mm. wide in a plane normal to the control edge formed by each groove, each groove being modified in accordance with the invention, being 0.1 mm. deep at a point 1 mm. from the control edge and having a base tapered in radial depth at an angle of 4 degrees both measured in a plane normal to the control edge. These proportions were such that an initial pressure of 700 kgm./sq. cm. would decay to a pressure of the order of kgm./ sq. cm. over 2.45 mm. of piston travel or in 2.7 milliseconds of time equivalent to 3.5 degrees of rotation of the cam operating the pump piston.

In operation, the additional factor of control available by means of the said plurality of steps provides scope for design to vary the pressure decay in a manner which is also a function of other factors such as engine speed and pump piston speed. One characteristic resulting from the new construction is that the closure time of the delivery valve is increased by at least 60%. This reduction in velocity helps to reduce the impact load of the valve on its seat and prevents excessive stress in the valve body. In the specific example quoted the valve closing time was increased from 1.2 to 2 milliseconds.

We claim:

1. A liquid fuel injection pump comprising a cylinder, a piston reciprocably mounted therein and defining a pumping chamber at one end thereof, an escape port in said cylinder, a channel formed in the periphery of said piston, a primary control edge along one side of said channel, said port and channel being in continuous communication with said chamber, the improvement characterized in that said channel has a bottom that is continuously sloping from the primary control edge towards the opposite limit of the escape channel, said channel initially defined by such primary control edge and so proportioned as to progressively vary the effective flow area through the complementary escape port in the cylinder wall to provide an instantaneous pressure decay rate of not more than 350 kgm/cmP/millisecond and not less than 70 kgm./cm. /millisecond.

2. A liquid fuel injection pump as claimed in claim 1 in which the primary control edge is of substantially helical form.

3. A liquid fuel injection pump as claimed in claim 1 in which the minimum radial depth of the channel is located at the primary control edge and increases progressively and continuously towards the opposite edge of the channel.

4. A liquid fuel injection pump as claimed in claim 1 in which the channel width varies along its length.

5. A liquid fuel injection pump as claimed in claim 1 in which means are provided to rotate the piston to vary the position of the control edge relative to said escape port in the pump cylinder wall.

6. A liquid fuel injection pump comprising a cylinder, a piston reciprocably mounted therein and defining a pumping chamber at one end thereof, an escape port in said cylinder, a channel formed in the periphery of said piston and extending generally helically thereon, a primary control edge along one side of said channel, said port and channel being in continuous communication with said chamber, means for effecting relative rotational positioning of the piston and cylinder to adjust the timing of relative register in the reciprocal movement of the piston to adjust the pump output for each stroke, the improvement characterized in that the channel has a base which becomes progressively continuously deeper from the piston periphery as the base extends away from that side of the channel along which the control edge is located.

References Cited UNITED STATES PATENTS 2,565,681 8/1951 Fleck et al 10341A 2,810,375 10/1957 Froehlich et al. l0337 3,435,770 4/1969 Ellis 103157 CARLTON R. CROYLE, Primary Examiner I. J. VRABLIK, Assistant Examiner 

